Kremkau Chapter 6 - Key Terms

Question 1

Aliasing

Answer 1

Improper Doppler-shift imfo from a pulsed-wave Doppler or color Doppler instrument when the true Doppler shift exceeds one half the pulse repetition frequency.

Question 2

Anechoic

Answer 2

Echo Free

Question 3

Comet tail

Answer 3

A series of closely spaced reverberation echoes.

Question 4

Cross-Talk

Answer 4

Leakage of strong signals in one direction channel of a Doppler receiver into the other channel; can produce the Doppler mirror-image.

Question 5

Enhancement

Answer 5

Increase in echo amplitude from reflectors that lie behind a weakly attenuation structure.

Question 6

Hypoechoic

Answer 6

Having relatively weak echoes. Opposite of hyperechoic (having relatively strong echoes).

Question 7

Mirror-Image

Answer 7

An artifactual gray-scale, color flow, or Doppler signal appearing on the opposite side (from the real structure of flow) of a strong reflector.

Question 8

Nyquist Limit

Answer 8

The Doppler-shift frequency above which aliasing occurs; one half the pulse repetition frequency.

Question 9

Reverberation

Answer 9

Multiple reflection.

Question 10

Slice thickness

Answer 10

Thickness of the scanned tissue volume perpendicular to the scan plane; also called section thickness.

Question 11

Shadowing

Answer 11

Reduction in echo amplitude from reflectors that lie behind a strongly reflecting or attenuating structure.

Question 12

Speckle

Answer 12

The granular appearance of images and spectral displays that is caused by the interference of echoes from the distribution of scatterers in tissue.

Question 13

Speed error

Answer 13

Propagation speed that is different from the assumed value (1.54 mm/us).